1. Field of the Invention
The present invention relates to a system and method for driving an electric vehicle and, more particularly, relates to a hybrid-type electric-vehicle-driving system with electric power generated by an internal combustion engine.
2. Description of Related Art
Japanese Patent Laid-Open Sho 60-1069 discloses a hybrid-type electric-vehicle-driving system with electric power generated from an internal combustion engine. Such an electric-vehicle-driving system is composed of a generator which is mechanically connected to a drive shaft of an internal combustion engine, an electric motor for driving vehicle wheels, battery unit for storing electric power of the generator and energizing the electric motor and a control unit for regenerating electric power by the electric motor when the vehicle speed is reduced.
However, since all the driving power of the above conventional system is applied to the wheels through electric power system including the generator, the battery unit and the motor, the power system is necessarily required to have a large size. In addition, since the energy conversion is made a plurality of times, the total efficiency of the system is not so high.
Japanese Patent Laid-Open Sho 58-130704 discloses a torque-speed converting system, in which engine power is converted into electromagnetic induction force and transmitted to the vehicle wheels by a wheel-drive motor having control coils and, as required, electric power is supplied from a battery to the wheel-drive motor, or kinetic energy of the vehicle is converted by the wheel-drive motor (functions as a generator) to electric power to be stored into a gyro wheel.
However, since the frequency of the induction current applied to the control coils (short-circuited coils) of the drive-motor is proportional to the engine rotational speed and can not be changed, it is not possible to control the rotational speed of the vehicle wheels although the torque can be changed.